Population estimates don't match up

NORTH COUNTY - Federal and state population analysts disagree on
how many people live in the cities of San Diego and Riverside
counties, and even whether the communities are in fact growing.

The disagreement is a consequence of the federal and state
governments using different methods to estimate populations, and
each is stubbornly clinging to its own. As a result, rather than
shedding light on growth and migration trends in area communities,
a new U.S. Census Bureau report being released today is perhaps
delivering more questions than answers.

Much is at stake with the numbers because the Census Bureau's
estimates are the basis for distributing federal funds and the
state Department of Finance's numbers are used to distribute state
funds.

The new federal government estimates suggest eight area cities
are losing population, while the state Department of Finance, which
also measures population, says that all those communities have
grown. The Census Bureau suggests Carlsbad, Escondido, Oceanside,
Murrieta and Temecula each have several thousand fewer residents
than the state credits them, and that San Diego has about 50,000
fewer residents.

Bill Schooling, a Department of Finance demographer, said gaps
between federal and state estimates tend to surface in the middle
of each decade. As several years pass after the most recent census,
when the federal government undertakes a massive door-to-door
campaign to yield a precise count of the nation's residents,
differences in estimating methods begin to yield different results,
he said.

But Schooling said the gap between federal and California
estimates has never been greater.

"We're puzzled," Schooling said. "There was certainly a gap in
the '90s, but it wasn't this large. So we're concerned."

Greg Harper, a demographer with the Census Bureau, said federal
officials are concerned as well, and have been trying to reconcile
the differences in population estimates in discussions with state
analysts.

So far, neither side has conceded ground.

"They certainly have capable demographers, as we do," Schooling
said. "But we believe that our numbers are better."

As for the new census estimates, Harper said the Census Bureau
believes "they are as accurate as they can be at this point."

Other analysts are hesitant to declare one approach to
estimating population better than another.

Laura Hill, research fellow with the Public Policy Institute of
California, said in a telephone interview from San Francisco that
neither of the estimates is "iron-clad accurate."

"They're just different," Hill said. "In the long run, we won'tknow who's right until the 2010 census comes out."

Hill was referring to the next time Census Bureau's workers will
fan out across the country to count people.

What is clear is where the gap comes from, both sides agree.

"It boils down to a different methodology," Schooling said.

The Census Bureau relies primarily on information gleaned from
tax returns, while the Department of Finance leans heavily on
driver's license address data and school enrollment information,
the demographers said.

"We think that (driver's license data) is a little more robust
of a data source," Schooling said. "We feel that they are likely to
be missing a lot of first-time (tax) filers."

Schooling also said the difference may indicate "changes in the
underground economy," including the number of people working or
employing workers without filing the appropriate tax forms.

But Harper defended the use of tax returns.

"It's the most complete data set that we have," he said.

Counting methods aside, the result is that as a general rule,
the state's estimates are higher than the Census Bureau's. That's
true even when adjusting for the fact that the bureau bases figures
on a July 1, 2006, snapshot, and that the Department of Finance
estimated populations as of Jan. 1.

In San Diego County, the bureau lists Oceanside's population as
165,803, Escondido's at 133,510 and Carlsbad's at 92,928. The
state's figures for each of those cities is significantly
higher.

In Riverside County, the bureau estimates Murrieta's population
at 90,457 and Temecula's at 89,392, well below state figures.

One of the biggest discrepancies involves the city of San Diego.
According to the federal government, the nation's eighth-largest
city has 1,256,951 residents. According to the state, the city's
population was 1,305,625 on Jan. 1, 2006, and 1,316,837 on Jan. 1
this year.

In another discrepancy, the new bureau estimates indicate that
Del Mar, Encinitas, Escondido, Oceanside, Poway, San Diego, Solana
Beach and Vista all lost population in the year leading up to last
July 1. The state maintains that each of those cities added
residents, although not many.

The Census Bureau's Harper said both sets of estimates indicate
that the seven cities have stable populations.

"I wouldn't put too much emphasis on a couple hundred going up
or down either way," Harper said.

When it comes to the raw numbers, state and federal estimates
track fairly closely for some communities. Examples include San
Marcos, Lake Elsinore and Poway.